1995-03-22_GENERAL DOCUMENTS - M1977451 (4)

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SR-I I (Ike #1 Mine) Designated Mining Operation January 31, 1995 - Page 4 The other important factor in solubility is the pH of the solution. As can be seen on the accompanying Eh-pH diagram for the U-OZ-HZO-CO2 system, "uranyl carbonate complexing causes a wide field of solubility to exist under conditions at all pH values" (Hostetler and Garrels, 1962 , p. 143) at low temperatures in both oxidizing and mildly reducing waters. Therefore, it appears that weathering of a uranium mine waste dump could produce a toxic uranium leachate. However, as Gableman put it, "the geologic problem for uranyl ions is not their mobility but their fixation in the low-temperature surficial environments" (Gableman, 1977, page 19) . It is a well established fact that uranium can be fixed by reduction of U+6 back to U+4. This is often done by organic compounds on which U+6 will absorb and later be reduced. This happens easier in acidic solutions than basic solutions. Other ways in which uranium is fixed, even without being reduced, are by absorption into clays and, at least temporarily, on fresh iron hydroxides. Even in the oxidizing environment, the uranyl ion, UOz+Z, will form many secondary minerals. In dry environments uranyl silicates, carbonates, and sulfates form by evaporation and are fairly stable at the surface as hydrated forms with Na, Mg, and Ca. Furthermore, U+6 will precipitate easily as phosphates, arsenates, and vanadates. The latter minerals are of the utmost importance in considering weathering of Salt Wash ores. Therefore, the geochemistry of vanadium will be discussed next. Vanadium generally occurs in nature in three valence states: V+3, the reduced state forms oxide minerals; V+4, in alumino-silicate minerals; and the V+5 oxidized state in the weathering cycle and in sedimentary rocks. Like uranium, during weathering vanadium is oxidized to soluble ions which are able to travel in solution over a wide range of acidity or alkalinity. Similarly, the presence of other components in an aqueous system controls the solubility of vanadium. Uranium oxidized to U+6 easier that vanadium does to V+5 all other conditions being the same. Although vanadium oxidizes similar to uranium, there are no known complexes between uranyl ions and vanadium to transport uranium, as there are with phosphates. Precipitation or fixation of vanadium can be brought about by several processes, including: 1) reducing agents such as organics or H2S, 2) presence of divalent cations of Pb, Zn, Cu which form insoluble compounds 3) by hydroxides of Al or ferric iron, and 4) precipitation of vanadates in the presence of divalent uranyl cations, (UO2) +2 . Even though vanadium is not scavenged by Fe and Mn oxides, as many other metals are in the secondary environment, it is generally concentrated in the ferruginous zone of soils in the V+5 state while V+3 will concentrate in the clay fraction. Although uranium and vanadium are each fairly soluble under similar oxidizing, either slightly acid or slightly alkaline conditions, together in the same natural solution, they will precipitate as the